On Wed, 9 Feb 2000, Rich Leggitt wrote:

> Something like this would work for two tasks in the same page. A more
> generic solution would be an interesting challenge but seemingly doable.
> Certainly this kind of thing is way more efficient than using explicit
> state machines.

if you're willing to add one variable for each task, you can stream line
this somewhat

switch macro _from_, _to_
       movlw  $+4
       movwf  _from_
       movf   _to_,w
       movwf  pcl
       endm

now the 18cxxx.... well there's probably a dozen ways to do this. I wish I
had time right now to explore them...

Scott

>
> context equ 0x20
>
> switch  macro                   ; macro to switch tasks
>         movlw $+2               ; load return 'return' address
>         goto dispatch
>         endm
>
>         org 0
>         goto 4
>         org 4
>
>         ; init task switcher
>         movlw task2             ; 'suspend' task 2
>         movw context
>         ; fall into task 1
>
> task1   do some stuff
>         switch
>         do some more stuff
>         switch
>         etc.
>         goto task1
>
>
> task2   do some stuff
>         switch
>         blah
>         goto task2
>
>
> dispatch
>         xorwf context,f         ; exchange w and context
>         xorwf context,w
>         xorwf context,f
>         movw pcl                ; jump to old context
>